Assuming SQL Server 2012 Standard with the latest service packs and updates.
What's wrong with just taking the Report Manager, slapping an SSL cert on it using the Reporting Configure Tool and then publishing it out to the Internet? Can that be done?
Note: All reports will require a Windows Logon. Anonymous access is not allowed.
JamesNT
"If you have to ask about various operating system limits, you're probably doing something wrong." -Raymond Chen